Clarence Leonard “Kelly” Johnson was an American aeronautical and systems engineer. He played a leading role in the design of over forty aircraft, including several honored with the prestigious Collier Trophy, acquiring a reputation as one of the most talented and prolific aircraft design engineers in the history of aviation.
He is recognized for his contributions to a series of important aircraft designs, most notably the Lockheed U-2 and SR-71 Blackbird.
In the below video you can see Johnson doing a walkaround of the SR-71, the powerful P&W J-58 turbo ramjets “that work as an ordinary turbojet up until about 1600 mph, then at that speed, it shift its actual cycle and becomes a ramjet”, the wing that “is a basic delta plan form with a conical camber which is a twist that gives us better crosswind landing characteristics and less drag when we go supersonic”.
Noteworthy is also the way Johnson talks about the chines, shaped so as to reduce the radar return of the aircraft that, as explained in a recent story, can somehow be considered the first stealth aircraft ante litteram.
Then, Johnson explains the aircraft’s peculiar movable conical spike used to change the inlet’s geometry. As we explained in detail in a previous article, the spike was used to control the supersonic air flow and position the shockwaves generated by the air slowing down into the throat of the inlet to obtain the best performance, while preventing the supersonic flow to reach the compressor.
The spike was in a full forward position during subsonic flight; above 30,000 feet and Mach 1.6 the spike started moving after into the throat to keep the shockwaves in the same optimum position. The spike moved approximatively one and 5/8 inches per 0.1 Mach, for a total maximum travel of 26 inches after into the inlet in the full retracted position.
We don’t know when this interview was filmed but it should be some time between 1975 (when Johnson retired) and 1983 (when he made one last known interview).
At the end of the clip Johnson says:
“I think it will be a long long time before we have an aircraft with higher performance than the SR-71”.
He was right: the last flight of an SR-71 took place on Oct. 9, 1999. Fourteen years later, in 2013, Lockheed Martin’s Skunk Works revealed the existence of a sort of SR-71 replacement: a Hypersonic intelligence, surveillance and reconnaissance (ISR) and strike aircraft dubbed SR-72, designed for Mach 6.
To date, the Mach 3+ SR-71 Blackbird remains the fastest, manned air-breathing aircraft ever produced.